The Cosmic Horseshoe

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This is an overview of my research into the gravitationally lensed galaxy named the Cosmic Horseshoe. This talk includes some background information as I have aimed this presentation at physics graduate students. Without additional explanation it is probably only suitable for an expert audience.

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The Cosmic Horseshoe

  1. 1. The Cosmic Horseshoe: The Rest-frame UV Spectrum of a z~2 LBG Anna Quider Institute of Astronomy University of CambridgeMax Pettini (IoA), Alice Shapley (UCLA), Charles Steidel (Caltech)
  2. 2. Today’s Talk ‣ Overview of Lyman Break Galaxies (LBGs) and rest-frame UV spectroscopy ‣ Results from the Cosmic Horseshoe - Stellar spectrum - Interstellar spectrum - Lyman alpha emission feature ‣ Broader conclusions from the Cosmic Horseshoe ‣ SummaryAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  3. 3. The Universe
  4. 4. The UniverseGalaxies from about 2 to 3 billion years after the Big Bang
  5. 5. What is a LBG?‣ High z starforming galaxy identified by the Lyman break photometric selection technique‣ Criteria for 2 ≤ z ≤ 2.5: R ≤ 25.5 G - R ≥ -0.2 G - R ≤ 0.2 (Un - G) +0.4 (Un - G) ≥ (G - R) + 0.2 (Un - G) ≤ (G - R) + 1.0 (Steidel et al. 2004) (Adelberger et al. 2004)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  6. 6. garding how the UV LF evolves at high redshift. While some stud- evolve ies have argued that the evolution primarily occurs at the bright (2006) Cosmic Context end (i.e., Dickinson et al. 2004; Shimasaku et al. 2005; Ouchi et al. 2004a; Bouwens et al. 2006, 2007; Yoshida et al. 2006), there from z of resu have been other efforts which have argued that the evolution oc- very st higher the UV ficient 2003, z k 7, numbe dropou 2007) Table 7 À20:5 (see al Stanwa bright The of UV et al. (2 (Bouwens et al. 2008) cluster Fig. 9.—Estimated star formation rate density as a function of redshift (inte- that a sAnna Quider down to 0.2 LÃ as in Fig. Horseshoe: UV of points give the SFR density grated The Cosmic 8). The lower set Spectrum z¼3 Institute of Astronomy al. ( et
  7. 7. garding how the UV LF evolves at high redshift. While some stud- evolve ies have argued that the evolution primarily occurs at the bright (2006) Cosmic Context end (i.e., Dickinson et al. 2004; Shimasaku et al. 2005; Ouchi et al. 2004a; Bouwens et al. 2006, 2007; Yoshida et al. 2006), there from z of resu have been other efforts which have argued that the evolution oc- very st higher the UV ficient 2003, z k 7, numbe dropou 2007) Table 7 À20:5 (see al Stanwa bright The of UV et al. (2 (Bouwens et al. 2008) cluster Fig. 9.—Estimated star formation rate density as a function of redshift (inte- that a sAnna Quider down to 0.2 LÃ as in Fig. Horseshoe: UV of points give the SFR density grated The Cosmic 8). The lower set Spectrum z¼3 Institute of Astronomy al. ( et
  8. 8. Local Galaxies Early Galaxies (Bouwens et al. 2008)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  9. 9. What’s visible in a galaxy? ga la xy Gas ? DustStars Also: planets, comets, asteroids...but too small to see
  10. 10. Studying Galaxies Using How can you study galaxies? Spectroscopy Using Spectroscopy! Light is split into its component wavelengths so that we galax can directly study the stars and gas in the galaxy galaxy? TextLight from stars y?Hot, ionized gas close to starsCold gas between stars Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  11. 11. Stars are Blackbodies Very red (cool)• Different wavelengths probe different stellar populations Very blue (hot)• Rest-frame UV spectroscopy probes the most massive, youngest stars Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  12. 12. Aside:Astronomy Naming Conventions Any element heavier than Hydrogen or Helium is called a “metal” (e.g. C, N, O, Fe, Ni, Si, etc.) O I = neutral oxygen O II = singly ionized oxygen O III = doubly ionized oxygen etc.Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  13. 13. Rest-frame Optical Spectra H II region emission lines are very visible and therefore are relatively easy to study (Erb et al. 2006a)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  14. 14. Rest-frame Optical SpectraMedian Values for z~2 LBGs SFR ~23 MO/yr Z 0.4 to 1.0 ZO E(B-V) 0.15 σ ~100 km/s Age 570 Myr M❋ 2 x 1010 MO (Erb et al. 2006a,b,c) (Erb et al. 2006a) Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  15. 15. Rest UV Spectral Features Low Ion IS Abs High Ion IS Abs Stellar Abs Nebular Em Stellar Em H I Em/Abs (Shapley et al. 2003) A mix of features from hot OB stars, low and high ionization interstellar gas, and the H II regionsAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  16. 16. What about a detailed study of the stars, interstellar gas, and H II regions in an individual LBG? The answer: Strongly gravitationally lensed LBGs!Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  17. 17. Gravitational LensingGravity distorts and magnifies light from distant galaxies Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  18. 18. MS1512-cB58‣ Serendipitously found in cluster MS1512+36 (z=0.37)‣ zcB58 = 2.7276‣ Magnified ~ 30x and L ~ L* Nitrogen (www.eso.org)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  19. 19. MS1512-cB58‣ Stellar population (metallicity, IMF)‣ Interstellar abundances Relative Flux‣ Large-scale outflows‣ Lyman-α feature morphology Relative Velocity (km s-1) Relative Flux α-capture Fe-peak Relative Velocity (km s-1) Nitrogen Figures from Pettini et al. 2002 Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  20. 20. Cosmic Horseshoe‣ 10” Einstein Ring‣ Discovered by Belokurov et al. (2007) in SDSS‣ 24±2x magnification (Dye et al. 2008)‣ L ≈ 2.4L*‣ zCH = 2.38115From rest-frame optical spectrum:‣ SFR = 100 MO/yr‣ Mvir ≈ 1.4 x 1010 MO‣ Z ≈ 0.5-1.5 ZO (Hainline et al. 2009)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  21. 21. ESI Spectrum‣Echellette Spectrograph and Imager (ESI) spectrum - Keck II telescope - 4000 - 10000 Å coverage (1184 - 2959 Å restframe) - 11.4 km s-1 pixel-1 resolution - 36100s total exposure - Spectra of two knots (Quider et al. 2009; courtesy of Dr. Lindsay King) Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  22. 22. 10 ly A high z star-forming galaxy has many regions like thisAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  23. 23. Hot, young stars Cavity caused by To Earth stellar wind 10 ly A high z star-forming galaxy has many regions like thisAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  24. 24. Hot, young stars Cavity caused by To Earth stellar wind 10 ly Gas being ionized by the young, hot stars (a H II region) A high z star-forming galaxy has many regions like thisAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  25. 25. Hot, young stars Cavity caused by To Earth stellar wind 10 ly Gas being ionized by the young, hot stars (a H II region) Cold interstellar gas (interstellar absorption) A high z star-forming galaxy has many regions like thisAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  26. 26. Stellar Photosphere “1425” “1978” “1425” Index: ‣ Blend of: - Si III 1417 - C III 1427 - Fe V 1430 ‣ ZOBstars = 0.5ZO “1978” Index: ‣ Only Fe III(Quider et al. 2009) Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  27. 27. Stellar Wind C IV Wind Feature(Quider et al. 2009) ‣ Complex superposition ‣ Wind due to most massive O stars- P-Cygni broad - narrow interstellar emission/absorption absorption ‣ Starburst99 models- photospheric broad - narrow nebular - Continuous SF absorption emission - 100Myr old - Salpeter IMFAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  28. 28. Stellar Wind ZOstars = 0.6ZOMS1512-cB58 andCosmic Horseshoe have very similar winds! (Quider et al. 2009) Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  29. 29. Interstellar Gas Absorption Normalized fluxAnna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  30. 30. Interstellar Gas Absorption Normalized flux Gas moving away Gas moving towards from the stars the starsStructure of the interstellar absorption lines is interpreted as being due to large-scale outflows of gas away from the stars Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  31. 31. Interstellar Gas Absorption ‣ -800 km/s to +250 km/s ‣ Same for low and high ionization gas ‣ Evidence for only ~60% coverage of stars by outflowing gas(Quider et al. 2009) Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  32. 32. Lyman α Emission Feature ‣ Lyman α is from H I gas ‣ Double-peaked emission ‣ Kinematic structure: - Peak 1 at +115 km/s - Peak 2 at +275 km/s - Red wing to +700 km/s(Quider et al. 2009)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  33. 33. aStructure matcheswell with outflow model from b Verhamme et al. (2006). cNHI ~ 7 x 1019 cm-2 λ Anna Quider λ The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  34. 34. What broader conclusions can we draw from studying the Cosmic Horseshoe?‣ Comparison between different metallicity indicators‣ Possible candidate for Lyman continuum photon leakage‣ A cautionary note on over-interpreting Lyα profiles Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  35. 35. Table 5. M Metallicity Indicators C ETALLICITY OMPARISON Method Element(s) Z/Z a Comments R23 O 1.5 H II regionsb N2 O 0.5 H II regionsb O3N 2 O 0.5 H II regionsb 1425 C, Si, Fe 0.5 Photospheric, OB stars c 1978 Fe ... Photospheric, B starsc C IV C, N, O, Fe ∼ 0.6 Stellar wind, O starsd(Quider et al. 2009) a Abundance relative to solar (on a linear scale), using the Good agreement abundances by Asplund et al. (2005). compilation of solar among different metallicity indicators b As reported by Hainline et al. (2009). c Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  36. 36. Lyman Continuum Photons C II 1334 O I 1302 Si II 1304‣ 10-15% of Lyman alpha photons escape‣ 60% covering of stars by interstellar gas may provide a route for the escape of Lyman continuum photons Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  37. 37. Lyman α Morphology Cosmic Horseshoe top 50% of LBGs Similarities Lyα emission Z~0.5ZO Salpeter IMF ΔvISM ~1000 km/s Relative Velocity Relative Flux (km s-1) (Quider et al. 2009)SFR~50-100 MO/yr MS1512-cB58Mvir~1-1.5x1010 MO top 25% of LBGs Lyα absorption Relative Velocity (km s-1) (Pettini et al. 2002)Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  38. 38. Summary • LBGs are high z starforming galaxies whose spectra show a wide variety of Lyα profiles, ISM trends with Lyα strength, young stellar populations, and gas with outflow speeds v ~ 200 km s-1 • Highly lensed LBGs are key to understanding the detailed chemical, kinematic, and structural properties of LBGs, as evidenced by the work on MS1512-cB58 and the Cosmic Horseshoe • More galaxies need detailed study to determine the range of properties of high redshift starforming galaxies: stay tuned for the Cosmic Eye, Cosmic Clone, and 8 o’clock Arc!Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  39. 39. Rest UV Spectral Features‣ Stellar Component: Best-fit Starburst99 model is 300Myr, continuous star formation, Z = 0.25 ZO‣ Interstellar Component: Absorption strength and Δvem-abs vary with Lyα emission strength for low- ionization transitions but are constant for high-ionization transitions‣ Physical Picture: Patches of neutral gas are embedded in a continuous shell of high-ionization gas, all of which is outflowing. (Shapley et al. 2003) (Steidel et al. 2003)A. Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy
  40. 40. Interstellar Gas Absorption (Quider et al. 2009)Column densities and ~0.5ZO imply N(H I) ≈ 6x1020 cm-2 A. Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

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